This invention relates to polyimide copolymers prepared by reacting a mixture of dianhydrides with a diamine. More specifically, it relates to polyimide copolymers prepared from a mixture of 4,4'-oxydiphthalic anhydride (ODPA) and 3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA) and either 4,4'-oxydianiline (ODA) or p-phenylenediamine (p-PDA).
Dianhydrides, such as ODPA, can be reacted with diamines to form polyimide resins. The formation of the polymer is a two step process. In the first step, the dianhydride reacts with the diamine to form a polyamic acid which generally remains in solution. The polyamic acid solution is then subjected to a curing process that includes heat. The solvent evaporates, and the polyamic acid releases water to form the final polyimide. Chemical methods of curing are also available.
There are several methods for forming objects from polyimides. For example, the polyamic acid solution can be spread on a surface and cured to form a film. The surface need not be flat. Alternatively, the polyamic acid solution can be cured to form the polyimide which can then be subjected to heat and pressure to form objects.
Polyimides were first prepared by T. M. Bogert et al. J. Am. Chem. Soc. (1908) 30, 1140. U.S. Pat. No. 2,710,853 discloses polyimides based upon pyromellitic acid. Polyimides based upon BPDA are disclosed in U.S. Pat. No. 4,247,443. The use of both BPDA and ODA in the preparation of polyimide polymers is disclosed in U.S. Pat. No. 4,290,936. Tim Tanunina, et al [Plast. Massy (9) 45-7, 1975 (in Russian)], describe polyimide copolymers prepared from 4,4'-diaminodiphenyl ether (ODA) and pairs of the following dianhydrides, pyromellitic dianhydrides (I); 3,3',4,4'-tetracarboxydiphenyl oxide (II); 3,3',4,4'-benzophenone tetracarboxylic acid (III); and 3,3',4,4'-diphenylsulfide tetracarboxylic acid (IV). The pairs of dianhydrides studied were II and III, I and II, and III and IV. The article discusses the glass transition temperature and densities of the copolymers formed, and compares them to the characteristics of homopolyimides.
Japanese Patent number SHO 63 [1988]-264121 discloses gas separation membranes prepared from polyimide polymers. The polyimides in question are copolymers containing ODPA and BPDA coupled with a variety of diamines, including ODA and para-phenylenediamine.
U.S. Pat. No. 3,416,994 discloses cross-linking polyimides and a process for producing them that comprises reacting a diamine and a dianhydride of a tetracarboxylic acid, the diamine or diester containing an aromatic keto group, and the diamine being present in an amount of at least 15% molar excess.
U.S. Pat. No. 3,520,837 discloses a method for making a polyimide foam from a tetracarboxylic acid ditertiary amine reaction product and an aromatic diamine in aqueous solution.
U.S. Pat. No. 3,528,950 discloses rapid-curing stable polyimides prepared by heating polyimide prepolymers having a specific terminal or endcapping chemical groups. The endcapping compounds are mono anhydrides that contain a double bond and become reactive at temperatures of about 200.degree. to 350.degree. C. A typical endcapping agent is 3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride.
U.S. Pat. No. 3,959,350 discloses melt fusible linear polyimides of aromatic primary diamines such as paradiamino benzene with 2,2-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride. In the preferred embodiment for extrusion and injection molding, a polyimide is characterized by amine end groups that are end capped with phthalic anhydride.
U.S. Pat. No. 4,537,947 discloses aromatic polyimides with various functional end groups such as --CH.dbd.CH.sub.2, --C.tbd.CH, --CN and --CHO that are chain-extended (molecular weight increased) by reacting the functional groups with aromatic bis-dipoles. A representative bis-dipole is 1,4-benzene-dinitrile oxide. These polyimides can be shaped and formed prior to chain extending. The aromatic polyimides appropriate for chain-extending are formed by the reaction of aromatic dianhydrides, with aromatic amines and monoamines that contain the functional groups.
Polyimides are used for wire insulation in certain specialized applications such as aircraft and spacecraft. Polyimides are also used in tape automated bonding (TAB) of semiconductor devices. In TAB semiconductor packaging, a thin sheet of copper is bonded to a polyimide film. The copper is etched to form leads and the semiconductor is then attached to the polyimide film. The leads on the TAB film may then be attached to the semiconductor. The TAB technology allows each chip to have a greater number of leads, and to be connected to the circuit board without having to drill holes through the board. In addition, TAB chips require less vertical space than conventional chips, and therefore, allow more compact circuitry. U.S. Pat. No. 4,063,993 discloses specific methods for bonding semiconductor leads to a tape and also discloses the use of polyimides as the basis of such a tape.